DEM Processing/Enhancement Example

A digital elevation model (DEM) is a raster-based digital dataset of the topography or terrain (hypsometry and/or bathymetry).  It is also widely known as a digital terrain model (DTM).  The DEM data is used to highlight structure related to topographic features and is also required for the calculation of the Isostatic correction in gravity processing.  For large data coverages and projects where DEM data is unavailable or incomplete, satellite topography data may be downloaded for project use.

SRTM30 Plus DEM - Elevation Colour TableSRTM30 Plus is a global DEM with a horizontal grid spacing of 30 arc-seconds (approximately 1 kilometre) comprising a combination of land data from the USGS SRTM30 gridded DEM data product created with data from the NASA Shuttle Radar Topography Mission, and ocean data based on the Smith and Sandwell global 1-minute grid.  All data are derived from public domain sources and these data are also in the public domain.  For details see the SRTM Homepage: http://www2.jpl.nasa.gov/srtm/

Standard Filters

AGC of SRTM30 Plus DEMThe automatic gain control (AGC) filter equalizes the range of amplitude variation across the grid. The filter highlights topography contrasts and sharpens variations in terrain.

1VD of SRTM30 Plus DEM

 The first vertical derivative (1VD) filter was applied to the topography grid in order to reduce regional effects and highlight surface topography. The 1VD shows short wavelength changes in slope which may be used to detect fault traces at surface. The colour image emphasises the contrast in the terrain.

Tilt of SRTM30 Plus DEThe Tilt filter (Tilt) significantly enhances subtle changes in areas of relatively flat topography and emphasizes the edges of broad topographic features.

MS Filter of SRTM30 Plus DEMThe Modulus (MS) or Horizontal Gradient Magnitude (HGM) filter is a tool for outlining the boundaries of topographic features where the peaks of the horizontal modulus indicate the edges of features.

FrOG Tech Proprietary Filters/imagery

ZS-edge of SRTM30 Plus DEMThe ZS-Edge filter is a FrOG Tech proprietary filter designed to map the edges of features.  The filter improves characterization and structural detail of topographic features by enhancing contrasts in areas of relatively flat topography response.

Ternary Image of Tilt, ZS-Edge & MS Filters of SRTM30 Plus DEM

The FrOG Tech proprietary CMY ternary image of the topography combines the results of the Tilt (cyan), ZS-Edge (magenta) and Modulus (yellow) enhancement filters to produce a highly detailed image of the topography. The enhancement image improves characterization and structural detail of topographic features by enhancing contrasts in areas of relatively flat topography response, and shows continuity of major structures, flat or steep, with strong or weak variations. This image is also of use in accurately locating features as no sun angle is applied to the image.

Ternary Image of Tilt, MS & AGC Filters of SRTM30 Plus DEM The FrOG Tech proprietary CMY ternary image of the topography combines the results of the Tilt (cyan), Modulus (magenta) and AGC (yellow) enhancement filters to produce a highly detailed image of the topography. The enhancement image highlights the edges of features, enhances subtle contrasts in areas of relatively flat topography response and shows continuity of major structures, flat or steep, with strong or weak variations. This image is also of use in accurately locating features as no sun angle is applied to the image.

Ternary Image of Tilt, MS & ZS-Edge Filters of SRTM30 Plus DEMThe FrOG Tech proprietary CMY ternary image of the topography combines the results of the Tilt (cyan), Modulus (magenta) and ZS-Edge (yellow) enhancement filters to produce a highly detailed image of the topography. The enhancement image improves characterization and structural detail of topographic features by enhancing contrasts in areas of relatively flat topography response, and shows continuity of major structures, flat or steep, with strong or weak variations. This image is also of use in accurately locating features as no sun angle is applied to the image.